Ideas for details at sculpting
Sculpters have the opportunity to directly model wrinkles and bumps into their hi-res models for automatic normal map generation, instead of trying to approximate them with hand drawn normal maps later. If you have the patience, you can do that now. As for the diffuse texture, if you want to paint it directly onto the model, you will get best results doing that on the low-poly mesh (you will need to unwrap the model first). To be clear, the high poly model does not need texture coordinates.

After both versions of the model are completely modeled and you have finished unwraping the UVs for the low poly mesh, you can bake the Normal map, Ambient Occlusion map and Curvature map (If you want those last 2 for smarter textures) from the hi poly onto the low poly.